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Author Topic: Tying into existing floor heat options?  (Read 66 times)

RSI

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Tying into existing floor heat options?
« on: November 30, 2017, 03:08:33 PM »

I have a project coming up soon where I need to hook up to an existing system.
The existing heat source is a wall hung on demand water heater with internal flow switch that fires the boiler when it senses flow.

I had planned on just adding a plate hx and mixing valve in series with the existing heater but with the flow switch, I don't think that will work. I am planning on putting a 3 way zone valve between the heater and pump and connect that to the heat exchanger and mixer and put a tee at the return to the heater for the plate hx return

Are there any other options that may be better? I though about using another pump instead of zone valve but then would need to add check valves too.
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Re: Tying into existing floor heat options?
« Reply #1 on: November 30, 2017, 03:43:22 PM »

How about a storage tank and run the circulator that triggers the heater off of storage tank temp?
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RSI

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Re: Tying into existing floor heat options?
« Reply #2 on: November 30, 2017, 05:41:56 PM »

I just thought of another option that I don't think I want to do because of the layout would be to put the gas heater on a secondary loop.
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wreckit87

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Re: Tying into existing floor heat options?
« Reply #3 on: November 30, 2017, 05:50:59 PM »

I have a quite similar one coming up here. My plan is to use a 50 gallon electric water heater as storage, but disable the elements so that when the temp sensor in the tank calls, it kicks on a pump drawing from the bottom of the tank and runs it across the plate HX and then through the electric boiler before depositing back to the tank. In both our cases, I think an aquastat in/on the line between HX and boiler/heater and wired in to override the flow switch unless the water is under 120 degrees or whatever, would work. Flow switch will make right away when the pump kicks in but if the aquastat is in series before getting back to the tankless, it should override the flow switch and keep it from firing. I think. Right? One could also put a 3 way right underneath the tankless in a P/S fashion operated from an aquastat that would divert flow through the tankless when temp gets low but otherwise would flow straight through the valve and tee. Most pumps have integral checks so that shouldn't be a huge dilemma. My application will leave the tank hot, with the mixer on the output of the tank to elongate the storage capability, and in a non-storage application I'd still put the mixer after the tankless regardless
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RSI

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Re: Tying into existing floor heat options?
« Reply #4 on: November 30, 2017, 06:03:10 PM »

I won't have room to put a tank in this one.

With that setup, couldn't you pump from the bottom of the tank, through the heat exchanger and back in the tank with the pump controlled off the tank thermostat and then do a completely separate loop through the tank for the radiant heat and not need a mixing valve?
I would think the thermostat in the tank could be set to whatever temp you want the water.
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wreckit87

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Re: Tying into existing floor heat options?
« Reply #5 on: November 30, 2017, 06:20:17 PM »

I won't have room to put a tank in this one.

With that setup, couldn't you pump from the bottom of the tank, through the heat exchanger and back in the tank with the pump controlled off the tank thermostat and then do a completely separate loop through the tank for the radiant heat and not need a mixing valve?
I would think the thermostat in the tank could be set to whatever temp you want the water.

Yes, I will have a separate loop with a second pump serving the floor. The purpose of the storage though, is to keep the short cycling to a minimum. So we'll want that tank as hot as possible and mix it on the way out to the floor. Kind of defeats the purpose of storage to keep it at desired circulating temp because it'll run all the time.

Without the tank though, you'd still be able to make it work with either option I mentioned earlier using the aquastat, either to lock out the flow switch or to activate the 3 way ZV and force it through the tankless instead of the primary loop. Option 1 would save the expense and ugly of an extra ZV you don't need
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